Analog actuators (such as lamps or valves) must be set to specific analog values (which, for example, are a measure of the lamp brightness or valve opening). Triggering of the actuators for specifying the desired analog values (which are often different or variable) is generally accomplished by means of pulse-width modulation: the analog value is defined by a specific pulse duty factor (ratio between on-time or pulse-time and duration of trigger period), the pulse duty factor is given by the counter reading on a digital counter, the counter output is switched over on reaching the counter reading and the actuator is triggered according to the switched state of the counter output. Optionally, the digital output signal of the counter can be smoothed (by a filter, for example) and a controllable direct current can be generated for current-dependent triggering of the actuator. Triggering of the actuators with variable analog values is accomplished by altering the pulse duty factor through variation of the on-time/pulse-time while maintaining a constant trigger signal period; it is possible here for the pulse duty factor to vary in discrete steps with the step width of the counter.
However, the problems associated with the method described above are:
the pulse duty factor must be loaded (into a memory, for example) after each trigger period; PA1 owing to the discrete steps of the counter and depending on specific characteristics pertaining to the system (for example, trigger signal period too long, counter step width too small, filter effect too slight) the on-times/off-times become noticeable (especially in the case of long no-pulse times or pulse times); PA1 an increase in the fundamental frequency or a reduction of the trigger signal period imposes a greater load on the pulse-width modulation and the effort required to set the required pulse duty factor increases.